http://www.cooperindustries.com/con...s/bus-ele-pp-10103-battery-separator.pdfThe 1314 unidirectional separator will combine the batteries when the engine battery hits 13.2 volts via alternator or charging surce attached to engine battery, and disconnect them when voltage falls, after engine shutdown, to 12.8v. It does not alternate between the two.
In my experience after engine starting, even with a well depleted engine battery, the voltage quickly hits 13.2v so I'd expect the batteries to be paralleled nearly instantly, or at least very quickly after engine starting.
How long it takes combined battery voltage, after driving, to fall the the 12.8v threshold, where it disconnects the batteries, is dependent on many variables, chief of which are battery state of charge, temperature, and any loads on the batteries.
the 1315 bi directional isolator combines the batteries when EITHER battery hits 13.2v, and disconnects them when their combined voltage falls to 12.8v.
The Bidirectional isolator is good for when the engine starting battery will be seeing loads, like from the dash stereo and dome lights and 12v powerports up there. If the engine battery is not discharged much at all, then the bidirectional relay might overcharge it, if it takes a long time to fully charge the house/aux battery.
The link says if engine battery is lower than Aux battery it will automatically combine them for starting. I was unaware of this feature.
No other isolation is required, and this isolator and most every other one, can be put near the house battery, it does not have to go in engine compartment.
Fusing.....
a large fuse, capable of passing starter motor current (~140 to 180 amps) should be within 7 inches of the battery (+), according to ABYC codes, american yacht and boat council. Some might consider this overkill in an automotive application.
If one stacks another ring terminal on the alternator(+) output stud, then there is already a fuse between engine battery and alternator. So ATL(+) to bussman, to Aux battery, there needs to be a fuse within 7 inches of the (+) post of Aux battery. This wiring method is usually a shorter path, circuit wise and distance wise, compared to taking power from engine starting battery.
Stacking another ring terminal on alternator (+) output stud is not always simply accomplished.
If one decides instead, to take power from the engine battery, and most will do, then the original alternator to engine battery cable has to take the load of not only the engine starting battery, but also the depleted Aux battery. This cabling was never intended to carry this much additional current. It could blow the existing fusible link/fuse, if not upgraded. If it does not blow the fuse there will be more voltage drop on that cabling, and voltage drop slows battery charging
If one does take power for isolator from engine battery, then there needs to be a fuse within 7 inches of the engine battery and again on the Aux battery, whereas if one takes power from the alternator (+ stud) then one need only one fuse at Aux battery as the original cable from alternator to engine battery is already fused.
The shorter circuit from alternator to common Aux battery location, means less copper and higher voltage reaching depleted Aux battery, which means faster recharging, but can also mean the alternator gets hotter faster and wears out sooner.
With either the 1314 or the 1315 isolator/separator in place, any loads placed on house battery will not be able to drain engine battery. No other product is required. Anything wired to original engine battery will still be able to draw down the engine battery, and apparently once it drawn 0.3v less than aux battery, will draw off the Aux battery too due to that engine start assist feature in the documentation. So it looks like leaving the headlights on engine off, can also draw down the house battery.
Bussman/cooper is re-labelling a Surepower 1314 or 1315 device. they might be had for cheaper elsewhere without that bussman name.
There are dozens of similar products on the market, and i have not researched all of them nor know if they employ a time delay, or use voltage sensing, or some combination of both in order to decide when and how they parallel or disconnect the batteries from each other.
One can fuse the house battery, at the house battery if they have a few more inches of height clearance:
https://www.amazon.com/Blue-Sea-Sys...d=1580506205&s=automotive&sr=1-2Note that links does not include the fuse itself, and they are not inexpensive. ANL fuses and holders can be gotten cheaper but require more wire terminations which introduces more potential failure points and voltage dropping resistance.
Fuses are to protect the wiring, so the proper fuse size is for the gauge of the wiring it is protecting. A battery fuse is more a catastrophic fuse, say in case the cable is pinched in an accident between frame members. One can overfuse and still be protected from catastrophic shorts of thick cables, and most vehicles do not have a fuse between starter and battery.
I am not saying the fuse necessity, can be ignored, though it seems many auto manufacturers do exactly that. Protect all (+) cables in some split loom and protect against chafing and vibration. (-) too, but these shorting to ground is not going to cause a fire.
A question you are sure to have in the not so distant future regards grounding of the house battery.
yes, one can run a thick cable from aux battery to nearby metal frame. When one does this all charging current to house battery must flow from original engine battery to firewall to battery or frame or battery to engine grounds. Frame engine and firewall grounds are the cause of many electrical gremlins.
It is my opinion that it is best, to run two cables to the alternator, from Aux battery, with isolator and fuse in the middle on the (+). If the alternator has a negative output stud already, use that, or a mounting bolt otherwise.
If one wants to use a nearby ground from house battery to metal frame, then I advise running a new ground cable from frame to alternator (-) stud or mounting bolt. If they do not want to do that then upgrade the original engine battery to engine ground cable, and might as well upgrade the engine battery to firewall ground at the same time.
A big Lifeline AGM battery, well depleted, can demand more than 100 amps from the alternator,IF, the cabling is thick(4awg or thicker) and the voltage regulator is seeking mid to high 14's and the cold 100 amp+ rated alternator is actually capable of delivering that much amperage at higher rpm, which is unlikely.
They have 200 amp models of isolator available but I think unless you go crazt with 1awg or thicker wire and more than one gpl-31xt battery, it is unnecessary.
Things can really be taken to extremes with systems such as these, and even the best alternator charging system is not going to defy physics.
80% charged to 100% charged cannot be accomplished in less than 3.5 hours, and that assumes mid 14's charging voltage is held that entire time, and the battery is still healthy. It takes longer when the battery is less healthy, and it could be significantly longer than that if the battery has seen many partial state of charge cycles, where it was discharged again without having ever reached full charge. I've witnessed that 80% to 100% take 7 hours, on a healthy battery that cycled 10 times only reaching 85% before the next discharge cycle began.
Lead acid batteries, which includes Gel and AGM, ideally, for maximum longevity and performance, ALWAYS want to be 100% charged, and kept relatively cool.
This basically means, if one wants good or better battery longevity, that one requires either solar, or plug in charging sources, which can have enough time at a high enough voltage, to actually bring the depleted battery to a true full state of charge.
So if one has enough battery power to get through a 3 day weekend, then one can forgo the battery isolator for house battery charging and plug in an adequate charging source on their return.
If one does not have enough battery capacity to meet their 3 day overnight needs, then alternator charging is highly desirable, and as many amps flowing into that depleted battery, as possible, is also desirable.
bateries below 80% state of charge can accept huge charging currents and get back to 80% state of charge quickly,with high amperage, but that 80% to 100% is what takes no less than 3.5 hours.
Don't discount the portable solar panel set-ups either. They can do a lot to replenish batteries and take stress off other charging systems.
I recently measured the output from a 100 watt flex panel On top of my windshield and then again behind it, facing south at noon, at the same angle, no shadows. 87 watts on top of windshield, 43 watts behind it.
My fridge compressor uses 32 watts........and runs 15 minutes per 60......
